1. Field of the Invention
The present invention relates, in general, to a coupling and, more particularly, to a reinforcing bar coupling which is intended to obtain a mechanical butt-joint between the ends of two reinforcing bars in reinforced concrete work to enhance the strength of the coupled portion and to afford a prompt and convenient coupling operation.
2. Related Prior Art
Since reinforcing bars are produced at certain unit lengths from factories, building works for various structures such as bridges, retaining walls and apartment houses, which extend to several tens of meters in length, require the ends of reinforcing bars to be overlapped. As conventional methods for joining reinforcing bars, a few joint processes are commonly used, which are disclosed as follows.
In the prior art, a lap-joint process, which is carried out in such a way that the ends of reinforcing bars are lapped along certain lengths thereof and the lapped ends of the reinforcing bars are bound with binding wires, is predominantly used. However, the lap-joint process has disadvantages in that distances between the adjacent reinforcing bars become small at the lapped regions, the required number of reinforcing bars is increased due to the lapped regions of the reinforcing bars, a pouring operation of concrete into space between the lapped reinforcing bars is difficult due to the small distances between the adjacent reinforcing bars, and the lap-jointed reinforcing bars are weakened in resistance to axial tensile force and compressive force.
In another process, i.e., in a gas pressure welding process in which the ends of reinforcing bars are butted to each other and the ends of the reinforcing bars are welded to each other by high temperature flame, a specialized technique is required to carry out the gas pressure welding process, the welded portion of the reinforcing bars is weakened by heat, and a post-welding inspection is further required.
In a steel pipe compression process in which the ends of two reinforcing bars are inserted into a steel pipe and the steel pipe containing the ends of two reinforcing bars is compressed by a hydraulic jack, though a specialized technique is not required, special equipment is required to perform the joining operation.
Therefore, to overcome the above problems, a process for mechanically joining two reinforcing bars has been developed and used in recent years.
In this process, the ends of reinforcing bars are subjected to a plastic deformation, i.e., thickened and shortened by hot or cold working, or the ends of reinforcing bars are subjected to cold swaging, causing the ribs of the bars to be collapsed and to be smooth, and then threaded with external threads (male) by a machine tool such as a screw thread rolling machine. Subsequently, the threaded ends of two reinforcing bars are threaded into a coupling having female threads in its internal surface, thereby joining the two reinforcing bars.
However, the above thread-joint process also has disadvantages in that it requires many working steps to form male threads on the ends of the reinforcing bars, and although reinforcing bars are considerably long and apt to be bent due to the material characteristics thereof, two reinforcing bars must be precisely aligned with each other to allow the ends of the reinforcing bars to be threaded into a coupling, thereby involving inconvenience in the joining operation.